Batches of polio vaccine from all the companies are to be tested to rule out contamination, drug regulator Dr S. Eswara Reddy has stressed in a letter sent on Wednesday to CDL, which is the national control laboratory for testing of immunobiologicals meant for human use in India.

“It has been asked that along with P1 and P3 strain, all the batches of biovalent vaccine be tested for identification of type 2 also," said one of the people cited above, requesting anonymity.

Traces of polio type 2 virus, a strain known to have been eradicated from India, were found in some batches of oral polio vaccine (OPV) manufactured by the Ghaziabad-based Bio-Med Pvt. Ltd, indicating the use of a vaccine containing type 2 poliovirus, despite such vaccines having been phased out globally in April 2016.

A three-member team constituted by the drug regulator also started its investigation into the issue on Wednesday.

“This detection indicates the use of a vaccine containing the type 2 poliovirus, despite the fact that vaccines containing type 2 poliovirus (trivalent oral polio vaccine) have been phased out globally and in India in April 2016 as a part of the polio end game strategy. As elsewhere, bivalent oral polio vaccine (bOPV) has replaced the trivalent OPV (tOPV) in all polio campaigns and routine immunization in India," a WHO official said.

The Union health ministry on Monday said that there was no need to panic and steps have been taken to deal with the aftermath of vaccine contamination. The ministry asked states to step up efforts to increase the immunization coverage in districts where contaminated vaccine has been used.

The ministry also directed the states to administer injectable polio vaccine (IPV) to those children who have not received it yet.

“Our regulatory and surveillance mechanisms are robust. Situation is under control and there is no need to panic," said a senior official in the health ministry.

The health ministry has drawn up an aggressive action plan to intensify their vaccination drive, Mission Indradhanush, and the states have been alerted, the official said.

“The districts have been identified and the children will be covered with IPV.

The contamination came to light about 15 days ago when the World Health Organization found signs of the virus in stool samples from surveillance reports from Uttar Pradesh. The samples were sent for testing, which confirmed contamination with type 2 virus.

“The case has not blown up to. As part of intensive surveillance, sewage samples are collected from 45 sites across eight states and tested for poliovirus in five accredited polio laboratories in the country. This is in addition to stool samples collected from individuals reporting sudden onset of paralysis or other polio like symptoms. Every year nearly 75,000 stool samples are collected and tested in polio laboratories in India. “This is when the WHO found type 2 polio vaccine virus in some sewage and stool samples during their routine surveillance,"the WHO official said. “The children are doing fine and the cases have not blown up to poliomylitesis," said the ministry official.

Directions have been given for the withdrawal of the vaccine manufactured by Bio-Med and recalled batches have been sent for testing to CDL, environmental surveillance has been strengthened," the official said.

India achieved a major success in its battle against polio after years of effort and was finally declared polio free in 2014. The last case was reported on 13 January 2011, when Rukhsar from Howrah was infected with type 1 polio virus.

The managing director of Bio-Med was arrested on Friday after the central drug regulator filed a FIR in the case. “It’s a non bailable offence, the managing director is behind bars and other directors, who are family members of the managing director, are absconding since," another official said.